Coriolis type mass flow meters are known in the art. In order to measure the weight of a material flow precisely, the effective Coriolis force or inertia force is measured. Such a force occurs when a moving mass particle is temporarily coupled with a rotating reference body. The resulting force is utilized for the mass determination. For this purpose, the material flow is directed onto a disk that is equipped with radially extending guide wings. The rotating disk with its guide wings makes sure that the flowable bulk material is diverted substantially radially, that is, perpendicularly to the rotational axis of the guide disk, whereby the bulk material is flung radially outwardly. The torque moment applied to the disk which rotates at a constant r.p.m. varies in accordance with the Coriolis force, whereby the torque variations are proportional to the respective mass flow.
An apparatus of the above type for the continuous weight measurement of a bulk material flow is described in German Patent Publication (DE-OS) 3,346,145 (Friedrich), published on Jul. 18, 1985.
In the known apparatus the winged disk or wheel is driven with a constant r.p.m. by an electric motor arranged axially directly above the winged wheel. The motor itself is mounted in a stationary housing in the manner of a pendulum. For this purpose a lever arm is secured to the drive motor which is pivotably mounted. The motor bears through the lever arm onto a force sensor such as a load cell secured to the housing, whereby the reaction torque moment of the occurring motor housing rotation is transmitted to the force sensor or load cell. The sensed force is multiplied by the length of the Lever arm to obtain the desired torque moment which corresponds precisely to the mass throughflow or throughput of the bulk material through the rotating disk. In the known apparatus the motor that is suspended in the manner of a pendulum, is guided by ballbearings relative to the stationary housing. Even though the friction in these ballbearings is small, such friction may still falsify the measurement of the torque moment. Even if the bearing friction is initially measured while no bulk material is running through the apparatus, and the respective "empty" measurement is taken into account subsequently, the measurement is not very precise because different frictions occur when the apparatus runs empty and when it runs while material is flowing through the apparatus. These bearing frictions can differ due to several factors. Such factors may include the one-sided mounting of the motor relative to the bearing walls, and a nonuniform lubrication, as well as a nonuniform distribution of the mass flow over the surface of the distribution disk, whereby the measuring results may be falsified.